1. Field of the Invention
The present invention relates to an optical disk apparatus for optically recording a signal on an information carrier using a light source such as, for example, laser and reproducing the recorded signal; and specifically to an optical disk apparatus including a focus controller for controlling a light beam directed onto the information carrier to constantly be in a prescribed convergence state.
2. Description of the Related Art
In this specification, the term xe2x80x9creproduction quality signalxe2x80x9d is defined as a signal representing the quality of a reproduction signal. The reproduction quality signal includes a jitter and a reproduction signal amplitude. The term reproduction signal amplitudes is defined as an amplitude of the reproduction signal. The term xe2x80x9creproduction signal amplitude measurement signalxe2x80x9d is defined as a signal representing the reproduction signal amplitude and is measured by a reproduction signal amplitude measuring section.
The characteristics expressed by the terms xe2x80x9cflat bottomed curvexe2x80x9d and xe2x80x9cflat topped curvexe2x80x9d are also expressed as xe2x80x9cflatxe2x80x9d.
The term xe2x80x9coptimum target positionxe2x80x9d is defined as a target position of a jitter characteristic at which the jitter is substantially minimum and a target position of a reproduction signal amplitude characteristic where the reproduction signal amplitude is substantially maximum.
One type of conventional optical disk apparatus, as described in, for example, Japanese Laid-Open Publication No. 2-135024, approximates a reproduction signal amplitude of a reproduction signal, changing relative to the target position of a focus control system, to a function for adjusting the target position so as to substantially maximize the reproduction signal amplitude. FIG. 18A is a block diagram illustrating a structure of a conventional optical disk apparatus 1800.
The optical disk apparatus 1800 includes an optical system 131 for directing light to form a beam spot (or beam) 111 on a disk 101, a disk motor 102 for rotating the disk 101 at a prescribed rotation rate, a light detector 109, preamplifiers 120A through 120D, a matrix calculator 121, a focus controller 132, a reproduction signal processing section 130, a DSP 1801, and a moving device 133. The optical system 131 includes a light source 103, a coupling lens 104, a polarization beam splitter 105, a polarization hologram device 106, a converging lens 107, and a collecting lens 108. The focus controller 132 includes a focus balance circuit 122 and a low pass filter (LPF) 123. The DSP 1801 includes a reproduction signal amplitude measuring section 1802, a target position searching section 1803, and a filter calculating circuit 134. The moving device 133 includes a focus actuator 127 and a focus driving circuit 126. The light detector 109 includes four light detecting sections 109A through 109D.
A light beam 110 emitted by the light source 104 is collimated by the coupling lens 104, and the collimated light is then reflected by the polarization beam splitter 105, passes through the polarization hologram device 106, and is converged by the converging lens 107 to form the beam spot 111 on an information track of the disk 101. The beam spot 111 reflected by the disk 101 passes through the converging lens 107, the polarization hologram device 106, and the polarization beam splitter 105, and is input to the light detector 109 through the collecting lens 108.
Outputs A through D from the four light detecting sections 109A through 109D are respectively input to preamplifiers 120A through 120D and processed with current-voltage conversion, and then are input to the matrix calculator 121. The matrix calculator 121 outputs a reproduction signal RF by adding all the outputs A through D ((A+D)+(B+C)), outputs a convergence state signal FS by (A+D)xe2x88x92(B+C), and outputs a phase difference tracking error signal (not shown) by comparing the phases of the signals (A+D) and (B+C). The reproduction processing circuit 130 detects an envelope of the reproduction signal RF and generates a reproduction signal amplitude measurement signal RFENV.
The focus control will be described. The focus balance circuit 122 subtracts a target position signal FBAL from the convergence state signal FS or adjusts a gain balance and thus inputs a focusing error signal FE to the filter calculation circuit 134 in the DSP 1801 through the LPF 123. The low pass filter 123 generates a focusing error signal FE by an astigmatic method based on the differential signal DS. The filter calculating circuit 134 executes filter calculations such as A/D conversion, addition, multiplication, and shift processing to the focusing error signal FE, and outputs a focus driving signal FOD. The focus driving circuit 126 current-amplifies the focus driving signal FOD. The focus actuator 127 drives the converging lens 107 so as to move the beam spot 111 in a direction perpendicular to the surface of the disk 101 based on the current-amplified focus driving signal FOD. Thus, the light beam on the disk 101 is controlled to be in a prescribed convergence state.
Measurement of the reproduction signal amplitude will be described. The reproduction signal processing section 130 generates a reproduction signal amplitude measurement signal RFENV based on the reproduction signal RF. The reproduction signal amplitude measuring section 1802 measures the level of the reproduction signal amplitude measurement signal RFENV by receiving the reproduction signal amplitude measurement signal RFENV by a built-in A/D converter (not shown) and performing digital sampling.
A method for adjusting the target position by the DSP 1801 shown in FIG. 18A will be described in detail with reference to FIGS. 18A and 18B. FIG. 18B shows a third-order function curve 1901 which approximates the relationship between the reproduction signal amplitude and the target positions, the relationship being obtained when the target position for focus control is moved step by step at a prescribed interval. Axis X represents the target position, and axle Y represents the reproduction signal amplitude. The reproduction signal amplitude measuring section 1802 moves through points A, B, C, D and E, which are provided at a prescribed interval, and measures the level of the reproduction signal amplitude measurement signal RFENV at each of the target positions. In order to enhance the precision of approximation, the reproduction signal amplitude measuring section 1802 measures the level of the reproduction signal amplitude measurement signal RFENV at the target positions interposing maximum point M on the reproduction signal amplitude characteristic.
Next, the relationship between the target position x and the reproduction signal amplitude y is approximated by function y=f(x). The reproduction signal amplitude characteristic is asymmetrical with respect to maximum point M as shown in FIG. 18B. In order to guarantee a sufficient approximation precision to the asymmetrical characteristic, approximation needs to be done with a third- or higher order function. By contrast, an excessively high order function complicates the calculation for approximation. Accordingly, the third-order function
f(x)=ax3+bx2+cx+dxe2x80x83xe2x80x83(1)
is optimum for approximating the reproduction signal amplitude characteristic.
There are various methods of approximation. For example, a least square method is usable. From equation (1),
ax3+bx2+cx+dxe2x88x92y=0xe2x80x83xe2x80x83(2)
is obtained. When target position xj and reproduction signal amplitude yj are actually substituted into equation (2), the value of 0 is not obtained by the influence of noise, a measuring error, or the like, and the following value is obtained.
a(xj)3+b(xj)2+cxj+dxe2x88x92yj=vjxe2x80x83xe2x80x83(2)xe2x80x2
When the values of a, b, c and d are set so that the total sum of the squares of vj, i.e.,       ∑          j      =      1        N    ⁢      xe2x80x83    ⁢            (      vj      )        2  
becomes minimum (N is a prescribed number of samples which is set), the curve 1901 represented by equation (1) passes through a position substantially close to the values actually measured by the reproduction signal amplitude measuring section 1802 (points A through E) as shown in FIG. 18B. Thus, a prescribed function y=f(x) can be calculated which approximates the relationship between the target position x and the reproduction signal amplitude y.
The reproduction signal amplitude measuring section 1802 stores a prescribed sample numbers N of target positions and reproduction signal amplitudes, and then executes the calculation so that the total sum of the squares of vj becomes minimum, thus to obtain approximate function y=f(x) The target position searching section 1803 calculates target XM corresponding to point M at which the reproduction signal amplitude y is maximum, i.e., maximum point M at function y=f(x). Target position XM at maximum point M is the optimum target position for focus control.
Then, a method for obtaining the maximum point will be described in detail. In the case of a third-order function, one maximum point and one minimum point are generally existent. The values on the x-coordinate of the maximum point and the minimum point are obtained as follows:
By differentiating the third-order function represented by equation (3), equation (4) is obtained.
y=ax3+bx2+cx+dxe2x80x83xe2x80x83(3)
yxe2x80x2=3ax2+2bx+cxe2x80x83xe2x80x83(4)
The values on the x-coordinate of the maximum point and the minimum point are the values of x in equation (4) when yxe2x80x2=0. Accordingly, by solving equation (5) using the quadratic formula, x1 and x2 are obtained as follows.
x1=[xe2x88x92b+{(b2xe2x88x923ac)}1/2]/(3a)xe2x80x83xe2x80x83(6)
x2=[xe2x88x92bxe2x88x92{(b2xe2x88x923ac)}1/2]/(3a)xe2x80x83xe2x80x83(6A)
Either one of x1 or x2 is the maximum point or the minimum point, and the other of x1 and x2 is the remaining of the maximum point or the minimum point. Due to the characteristic of the third-order function, when there are both the maximum point and the minimum point, the value of y of the maximum point is necessarily larger than the value of y of the minimum point. Accordingly, when x1 and x2 above are substituted into the original third-order function to obtain y1 and y2, and the values of y1 and y2 are compared, it can be determined which one of (x1, y1) or (x2, y2) corresponds to the maximum point. For example, when y1 greater than y2, x1 corresponding to y1 is the x-coordinate of the maximum point. After the reproduction signal amplitude measuring section 1802 obtains the approximate function, the target position searching section 1803 can obtain the values of x of the maximum point and the minimum point by executing the calculation represented by equations (6) and (6A). By comparing the values of y obtained based on the values of x, the value of x of the maximum point can be obtained.
As described above, in the conventional art, after the value of x of the maximum point is obtained, the reproduction signal amplitude measuring section 1802 outputs the value of x to the focus balance circuit 122 an the target position variable signal FBAL so as to optimize the convergence state of the light beam on the recording medium 101, i.e., the target position of focus control.
With reference to FIGS. 19A and 19B, an optical disk apparatus for approximating the jitter, which changes with respect to the target position, to the function and adjust the target position so as to substantially minimize the jitter will be described.
FIG. 19A is a block diagram of an optical disk apparatus 1800A. Identical elements previously discussed with respect to FIG. 18A bear identical reference numerals and the descriptions thereof will be omitted.
The optical disk apparatus 1800A shown in FIG. 19A is different from the optical disk apparatus 1800 in FIG. 18A in that the optical disk apparatus 1800A includes a jitter detector 124 and a DSP 1801A. The DSP 1801A includes a jitter measuring section 1802A, a target position searching section 1803A, and a filter calculating circuit 134.
FIG. 19B shows a third-order function curve 1902 which approximates the relationship between the jitter and the target position. Referring to FIGS. 19A and 19B, the jitter measuring section 1802A, like the reproduction signal amplitude measuring section 1802, moves the target position from point A to point B, C, D and E. The jitter measuring section 1802A measures a jitter signal JIT at each of the target positions. The target position searching section 1803A, like the target position searching section 1803 in FIG. 18A, approximates the relationship between the target position x and the jitter y with function y=ax2+bx2+cx+d, and thus obtains minimum point M and optimum target position XM. The target position searching section 1803 in FIG. 18A obtains the optimum target position based on the maximum value of the reproduction signal amplitude, whereas the target position searching section 1803A in FIG. 19A obtains the optimum target position based on the minimum value of the jitter.
According to the above-mentioned conventional art, the optimum target position at which the jitter is substantially minimum or the reproduction signal amplitude is substantially maximum is obtained in the following manner. The results of sampling is approximated to function 2001 (FIG. 20A) or 2101 (FIG. 21A), and minimum point M1 of the function 2001 or maximum point M2 of the function 2101 is obtained. An optimum target position 2002 corresponding to minimum point M1 of the function 2001 or an optimum target position 2102 corresponding to maximum point M2 of the function 2101 is obtained. Such conventional art has the following problems.
(1) As shown in FIGS. 20B and 21B, when a waveform equivalent circuit (equalizer; not shown) built in the reproduction signal processing section 130 has a characteristic which is excessively over-equalized (emphasized) or defocused due to the optical aberration or the like to be more influenced by crosstalk, a jitter characteristic 2003 and a reproduction signal amplitude characteristic 2103 exhibit a flat bottomed curve or a flat topped curve, i.e., the jitter or reproduction signal amplitude changes little in the vicinity of the point of inflection M2 or M3 with respect to the target position.
In order to specify the point of inflection M2 or M3, the number of points of measurement of the jitter or reproduction signal amplitude can be increased in order to improve the measuring precision. However, an increased number of points of measurement extends the time period for measurement.
Even when the optimum target position at which the jitter is minimum or the reproduction signal amplitude is maximum can be specified by increasing the number of points of measurement, the following problem is still involved. When the jitter characteristic or the reproduction signal amplitude characteristic are steep on one of the sides interposing the maximum or minimum point as a characteristic 2004 (FIG. 20C) or 2104 (FIG. 21C) and an optimum target position 2005 corresponding to minimum point M4 or an optimum target position 2105 corresponding to maximum point M5 is set, the margin on the one side is very small. In a worst case, the focus control is destabilized during the adjustment.
(2) In the case of an optical disk, such as a DVD-RAM disk, having a convex land track and a concave groove track which have information recorded therein, the jitter or reproduction signal amplitude characteristic with respect to the target position is significantly different between the land track and the groove track due to factors such as, for example, optical aberration and beam profile. For example, as shown in FIG. 22, a jitter characteristic 2201 of the land track exhibits a flat bottomed curve with little change in the vicinity of point of inflection ML. A jitter characteristic 2202 of the groove track exhibits a sharp inverted parabolic curve with respect to point of inflection MG at the center. Accordingly, the optimum target position needs to be set independently for the land track and the groove track.
It is not problematic to set optimum target positions FL and FG independently for the land track and the groove track. When, an shown in FIG. 23A, the difference between the optimum target positions FL and FG is large, a undulated focusing error response 2301 (FIG. 23B), a undulated jitter response 2302 (FIG. 23C), or a undulated reproduction signal amplitude response 2303 (FIG. 23D) occurs immediately after time t23 when the land track is switched to the groove track. As a result, information in a sector immediately after switching cannot be reproduced.
In the case where the deviation from the recorded layer perpendicular to the reference plane is large, the optimum target position changes during one rotation. Accordingly, the optimum target position based on the jitter or reproduction signal amplitude of one rotation may undesirably have an error with respect to the actual optimum target position. Due to the error, information stored in a portion where the deviation from the recorded layer perpendicular to the reference plane is largest cannot be reproduced.
An optical disk apparatus according to the present invention includes a converging section for converging a light beam toward an information carrier, a moving section for moving the light beam converged by the converging section in a direction perpendicular to a surface of the information carrier; a light detector for detecting the light beam reflected by the information carrier; a convergence state detecting section for generating a convergence state signal representing a convergence state of the light beam at a convergence point on the information carrier and outputting a reproduction signal from the information carrier, based on the output from the light detector; a focus controller for driving the moving section to make the convergence state constant based on the convergence state signal and a prescribed target position; a reproduction quality signal detector for detecting a reproduction quality signal representing a quality of the reproduction signal based on the reproduction signal; a reproduction quality signal measuring section for changing the target position and measuring a value of the reproduction quality signal corresponding to each of the changed target positions; a reproduction quality signal characteristic determining section for determining a characteristic of the reproduction quality signal based on the value of the reproduction quality signal corresponding to each of the changed target positions; and a target position searching section for searching for an optimum target position of the focus controller for optimizing the value of the reproduction quality signal based on a determination result of the reproduction quality signal characteristic determining section.
In one embodiment of the invention, the reproduction quality signal characteristic determining section determines, based on the value of the reproduction quality signal measured by the reproduction quality signal measuring section, whether or not the reproduction quality signal has a substantially maximum or minimum value in a prescribed range of the target positions. The target position searching section includes a first target position searching section for searching for the optimum target position when the reproduction quality signal has one of a parabolic characteristic or an inverted parabolic characteristic having the maximum or minimum value in the prescribed range, and a second target position searching section for searching for the optimum target position when the reproduction quality signal has a flat characteristic not having the maximum or minimum value in the prescribed ranges
In one embodiment of the invention, the first target position searching section includes a first control section for moving the target position in a direction in which a quality represented by the reproduction quality signal is presumed to be improved while searching for the optimum target position. The second target position searching section includes a second control section for moving the target position in a prescribed direction.
In one embodiment of the invention, the first target position searching section includes a function approximation section for finding an approximate function for approximating the relationship between the target position and the reproduction quality signal, and determines the optimum target position based on the approximate function. The second target position searching section determines the optimum target position by finding a center point in a portion of the prescribed range, in which a change in the value of the reproduction quality signal is restricted at a prescribed level or less.
In one embodiment of the invention, the second target position searching section restricts the portion to a prescribed area or less.
In one embodiment of the invention, the first target position searching section includes an approximate function determining section for obtaining an approximation degree between the approximate function obtained by the function approximation section and a prescribed shape of the characteristic of the reproduction quality signal. When the approximation degree is a prescribed level or more, the first target position searching section obtains the target position at which the value of the reproduction quality signal measured by the reproduction quality signal measuring section is substantially maximum or minimum as the optimum target position, without using the approximate function.
In one embodiment of the invention, when the reproduction quality signal characteristic determining section determines that the reproduction quality signal has a flat characteristic not having a substantially maximum or minimum value, the reproduction quality signal measuring section changes the target position with narrower steps and measures a value of the reproduction quality signal corresponding to each of the changed target positions.
In one embodiment of the invention, the information carrier includes a concave information track having a concave shape and a convex information track having a convex shape. The reproduction quality signal characteristic determining section includes a concave portion reproduction quality signal characteristic determining section for determining the characteristic of the reproduction quality signal based on the value of the reproduction quality signal corresponding to each of the target positions changed in the concave information track, and a convex portion reproduction quality signal characteristic determining section for determining the characteristic of the reproduction quality signal based on the value of the reproduction quality signal corresponding to each of the target positions changed in the convex information track. The target position searching section searches for a concave optimum target position at which the reproduction quality signal has an optimum value based on a determination result of the concave portion reproduction quality signal characteristic determining section, and also searches for a convex optimum target position at which the reproduction quality signal has an optimum value based on a determination result of the convex portion reproduction quality signal characteristic determining section.
In one embodiment of the invention, the concave portion reproduction quality signal characteristic determining section determines, based on the value of the reproduction quality signal in the concave information track measured by the reproduction quality signal measuring section, whether or not the reproduction quality signal in the concave portion has a substantially maximum or minimum value in a prescribed range of the target positions. The convex portion reproduction quality signal characteristic determining section determines, based on the value of the reproduction quality signal in the convex information tract measured by the reproduction quality signal measuring section, whether or not the reproduction quality signal in the convex portion has a substantially maximum or minimum value in a prescribed range of the target positions. The target position searching section includes a first target position searching section for searching for the optimum target position when the reproduction quality signal has one of a parabolic characteristic and an inverted parabolic characteristic having the maximum or minimum value in the prescribed range, and a second target position searching section for searching for the optimum target position when the reproduction quality signal has a flat characteristic not having the maximum or minimum value in the prescribed range.
In one embodiment of the invention, the first target position searching section includes a first control section for moving the target position in a direction in which a quality represented by the reproduction quality signal is presumed to be improved while searching for the optimum target position. The second target position searching section includes a second control section for moving the target position in a prescribed direction.
In one embodiment of the invention, the first target position searching section includes a function approximation section for finding an approximate function for approximating the relationship between the target position and the reproduction quality signal, and determines the optimum target position based on the approximate function. The second target position searching section determines the optimum target position by finding a center point in a portion of the prescribed range, in which a change in the value of the reproduction quality signal is restricted at a prescribed level or less.
In one embodiment of the invention, the target position searching section includes a concave portion target position searching section for searching for a concave portion optimum target position at which the reproduction quality signal has an optimum value based on a determination result of the concave portion reproduction quality signal characteristic determining section, a convex portion target position searching section for searching for a convex portion optimum target position at which the reproduction quality signal has an optimum value based on a determination result of the convex portion reproduction quality signal characteristic determining section, and a common target position calculating section for calculating a common target position usable in the concave information track and the convex information track, based on the concave portion optimum target position and the convex portion optimum target position.
In one embodiment of the invention, the common target position calculating section calculates a center position between the concave portion optimum target position and the convex portion optimum target position as the common optimum target position.
In one embodiment of the invention, the common target position calculating section determines the common optimum target position based on a value of the reproduction quality signal corresponding to the concave portion optimum target position and a value of the reproduction quality signal corresponding to the convex portion optimum target position.
In one embodiment of the invention, when either one of the concave portion reproduction quality signal characteristic determining section and the convex portion reproduction quality signal characteristic determining section determines that the reproduction quality signal has one of a parabolic characteristic and an inverted parabolic characteristic having a substantially maximum or minimum value in the prescribed range, the common target position calculating section determines the optimum target position found by the target position searching section corresponding is to the reproduction quality signal characteristic determining section which determined that the reproduction quality signal has one of the parabolic characteristic and the inverted parabolic characteristic, as the common optimum target position.
In one embodiment of the invention, the common target position calculating section compares a first reproduction quality signal measured by the reproduction quality signal measuring section when the target position is moved from the concave portion optimum target position and a second reproduction quality signal measured by the reproduction quality signal measuring section when the target position is moved from the convex portion optimum target position. When the first reproduction quality signal does not have a better characteristic than that of the second reproduction quality signal, the common target position calculating section determines the concave optimum target position as the common optimum target position; and when the first reproduction quality signal has a better characteristic than that of the second reproduction quality signal, the common target position calculating section determines the convex optimum target position as the common optimum target position.
In one embodiment of the invention, the reproduction quality signal includes jitter. The reproduction quality signal detector includes a jitter detector for detecting a jitter based on the reproduction signal. The reproduction quality signal measuring section includes a jitter measuring section for measuring a jitter value corresponding to each of the changed target positions. The reproduction quality signal characteristic a determining section includes a jitter characteristic determining section for determining a characteristic of the jitter based on the jitter value. The target position searching section searches for an optimum target position at which the jitter has a substantially minimum value based on a determination result of the jitter characteristic determining section.
In one embodiment of the invention, the jitter characteristic determining section determines, based on the jitter value measured by the jitter measuring section, whether or not the jitter has a substantially minimum value in a prescribed range of the target positions. The target position searching section includes a first target position searching section for searching for the optimum target position when the jitter has an inverted parabolic characteristic having the minimum value in the prescribed range, and a second target position searching section for searching for the optimum target position when the jitter has a flat bottomed curve characteristic not having the minimum value in the prescribed range.
In one embodiment of the invention, the first target position searching section includes a first control section for moving the target position in a direction in which the jitter is presumed to be decreased while searching for the optimum target position. The second target position searching section includes a second control section for moving the target position in a prescribed direction.
In one embodiment of the invention, the first target position searching section includes a function approximation section for finding an approximate function for approximating the relationship between the target position and the jitter value, and determines the optimum target position based on the approximate function. The second target position searching section determines the optimum target position by finding a center point in a portion of the prescribed range, in which a change in the jitter value is restricted at a prescribed level or less.
In one embodiment of the invention, the second target position searching section restricts the portion to a prescribed area or less.
In one embodiment of the invention, when the jitter characteristic determining section determines that the jitter has a flat bottomed curve characteristic not having a substantially minimum value, the jitter measuring section changes the target position with narrower steps and measures a jitter value corresponding to each of the changed target positions.
In one embodiment of the invention, the first target position searching section includes an approximate function determining section for obtaining an approximation degree between the approximate function obtained by the function approximation section and a prescribed shape of the characteristic of the jitter. When the approximation degree is a prescribed level or more, the first target position searching section obtains the target position at which the jitter value measured by the jitter measuring section is substantially minimum as the optimum target position, without using the approximate function.
In one embodiment of the invention, the information carrier includes a concave information track having a concave shape and a convex information track having a convex shape. The jitter characteristic determining section includes a concave portion jitter characteristic determining section for determining the characteristic of the jitter based on the jitter value corresponding to each of the target positions changed in the concave information track, and a convex portion jitter characteristic determining section for determining the characteristic of the jitter based on the jitter value corresponding to each of the target positions changed in the convex information track. The target position searching section searches for a concave optimum target position at which the jitter has an optimum value based on a determination result of the concave portion jitter characteristic determining section, and also searches for a convex optimum target position at which the jitter has an optimum value based on a determination result of the convex portion jitter characteristic determining section.
In one embodiment of the invention, the concave portion jitter characteristic determining section determines, based on the jitter value in the concave information track measured by the jitter measuring section, whether or not the jitter in the concave portion has a substantially minimum value in a prescribed range of the target positions. The convex portion jitter characteristic determining section determines, based on the jitter value in the convex information track measured by the jitter measuring section, whether or not the jitter in the convex portion has a substantially minimum value in a prescribed, range of the target positions. The target position searching section includes a first target position searching section for searching for the optimum target position when the jitter has an inverted parabolic characteristic having the minimum value in the prescribed range, and a second target position searching section for searching for the optimum target position when the jitter has a flat bottomed curve characteristic not having the minimum value in the prescribed range.
In one embodiment of the invention, the first target position searching section includes a first control section for moving the target position in a direction in which the jitter is presumed to be decreased while searching for the optimum target position. The second target position searching section includes a second control section for moving the target position in a prescribed direction.
In one embodiment of the invention, the first target position searching section includes a function approximation section for finding an approximate function for approximating the relationship between the target position and the jitter, and determines the optimum target position based on the approximate function. The second target position searching section determines the optimum target position by finding a center point in a portion of the prescribed range, in which a change in the jitter value is restricted at a prescribed level or less.
In one embodiment of the invention, the target position searching section includes a concave portion target position searching section for searching for a concave portion optimum target position at which the jitter has an optimum value based on a determination result of the concave portion jitter characteristic determining section, a convex portion target position searching section for searching for a convex portion optimum target position at which the jitter has an optimum value based on a determination result of the convex portion jitter characteristic determining section, and a common target position calculating section for calculating a common target position usable in the concave information track and the convex information track, based on the concave portion optimum target position and the convex portion optimum target position.
In one embodiment of the invention, the reproduction quality signal includes a reproduction signal amplitude measurement signal. The reproduction quality signal detector includes a reproduction signal processing section for detecting a reproduction signal amplitude based on the reproduction signal. The reproduction quality signal measuring section includes a reproduction signal amplitude measuring section for measuring a reproduction signal amplitude value corresponding to each of the changed target positions. The reproduction quality signal characteristic determining section includes a reproduction signal amplitude characteristic determining section for determining a characteristic of the reproduction signal amplitude based on the reproduction signal amplitude value. The target position searching section searches for an optimum target position at which the reproduction signal amplitude has a maximum value based on a determination result of the reproduction signal amplitude characteristic determining section.
In one embodiment of the invention, the reproduction signal amplitude characteristic determining section determines, based on the reproduction signal amplitude measured by the reproduction signal amplitude measuring section, whether or not the reproduction signal amplitude has a substantially maximum value in a prescribed range of the target positions. The target position searching section includes a first target position searching section for searching for the optimum target position when the reproduction signal amplitude has a parabolic characteristic having the maximum value in the prescribed range, and a second target position searching section for searching for the optimum target position when the reproduction signal amplitude has a flat topped curve characteristic not having the maximum value in the prescribed range.
In one embodiment of the invention, the first target position searching section includes a first control section for moving the target position in a direction in which the reproduction signal amplitude is presumed to be increased while searching for the optimum target position. The second target position searching section includes a second control section for moving the target position in a prescribed direction.
In one embodiment of the invention, the first target position searching section includes a function approximation section for finding an approximate function for approximating the relationship between the target position and the reproduction signal amplitude value, and determines the optimum target position based on the approximate function. The second target position searching section determines the optimum target position by finding a center point in a portion of the prescribed range, in which a change in the reproduction signal amplitude value is restricted at a prescribed level or less.
In one embodiment of the invention, the second target position searching section restricts the portion to a prescribed area or less.
In one embodiment of the invention, when the reproduction signal amplitude characteristic determining section determines that the reproduction signal amplitude has a flat topped curve characteristic not having a substantially maximum value, the measuring section changes the target position with narrower steps and measures a reproduction signal amplitude value corresponding to each of the changed target positions.
In one embodiment of the invention, the first target position searching section includes an approximate function determining section for obtaining an approximation degree between the approximate function obtained by the function approximation section and a prescribed shape of the characteristic of the reproduction signal amplitude. When the approximation degree is a prescribed level or more, the first target position searching section obtains the target position at which the reproduction signal amplitude value measured by the reproduction signal amplitude measuring section is substantially maximum as the optimum target position, without using the approximate function.
In one embodiment of the invention, the information carrier includes a concave information track having a concave shape and a convex information track having a convex shape. The reproduction signal amplitude characteristic determining section includes a concave portion reproduction signal amplitude characteristic determining section for determining the characteristic of the reproduction signal amplitude based on the reproduction signal amplitude value corresponding to each of the target positions changed in the concave information track, and a convex portion reproduction signal amplitude characteristic determining section for determining the characteristic of the reproduction signal amplitude based on the reproduction signal amplitude value corresponding to each of the target positions changed in the convex information track. The target position searching section searches for a concave optimum target position at which the reproduction signal amplitude has an optimum value based on a determination result of the concave portion reproduction signal amplitude characteristic determining section, and also searches for a convex optimum target position at which the reproduction signal amplitude has an optimum value based on a determination result of the convex portion reproduction signal amplitude characteristic determining section.
In one embodiment of the invention, the concave portion reproduction signal amplitude characteristic determining section determines, based on the reproduction signal amplitude value in the concave information track measured by the reproduction signal amplitude measuring section, whether or not the reproduction signal amplitude in the concave portion has a substantially maximum value in a prescribed range of the target positions. The convex portion reproduction signal amplitude characteristic determining section determines, based on the reproduction signal amplitude value in the convex information track measured by the reproduction signal amplitude measuring section, whether or not the reproduction signal amplitude in the convex portion has a substantially maximum value in a prescribed range of the target positions. The target position searching section includes a first target position searching section for searching for the optimum target position when the reproduction signal amplitude has a parabolic characteristic having the maximum value in the prescribed range, and a second target position searching section for searching for the optimum target position when the reproduction signal amplitude has a flat topped curve characteristic not having the maximum value in the prescribed range.
In one embodiment of the invention, the first target position searching section includes a first control section for moving the target position in a direction in which the reproduction signal amplitude is presumed to be increased while searching for the optimum target position and the second target position searching section includes a second control section for moving the target position in a prescribed direction.
In one embodiment of the invention, the first target position searching section includes a function approximation section for finding an approximate function for approximating the relationship between the target position and the reproduction signal amplitude, and determines the optimum target position based on the approximate function. The second target position searching section determines the optimum target position by finding a center point in a portion of the prescribed range, in which a change in the reproduction signal amplitude value is restricted at a prescribed level or less.
In one embodiment of the invention, the target position searching section includes a concave portion target position searching section for searching for a concave portion optimum target position at which the reproduction signal amplitude has an optimum value based on a determination result of the concave portion reproduction signal amplitude characteristic determining section, a convex portion target position searching section for searching for a convex portion optimum target position at which the reproduction signal amplitude has an optimum value based on a determination result of the convex portion reproduction signal amplitude characteristic determining section, and a common target position calculating section for calculating a common target position usable in the concave information track and the convex information track, based on the concave portion optimum target position and the convex portion optimum target position.
In one embodiment of the invention, the optical disk apparatus further includes a recording distinguishing section for distinguishing whether or not information is recorded on the information carrier based on the. reproduction quality signal detected by the reproduction quality signal detector, wherein the reproduction quality signal measuring section changes the target position based on a distinguishment result of the recording distinguishing section.
In one embodiment of the invention, when the recording distinguishing section distinguishes that the information is recorded on the information carrier, the reproduction quality signal measuring section changes the target position.
In one embodiment of the invention, the information carrier includes a concave information track having a concave shape and a convex information track having a convex shape. The reproduction quality signal measuring section changes the target position in the concave information track a first number of times, the first number corresponding to a first sample number which represents the number of samples of the reproduction quality signal measured in the concave information track. and changes the target position in the convex information track a second number of times, the second number corresponding to a second sample number which represents the number of samples of the reproduction quality signal measured in the convex information track. The first sample number and the second sample number are substantially equal to each other.
In one embodiment of the invention, the information carrier includes a concave information track having a concave shape and a convex information track having a convex shape. The reproduction quality signal measuring section changes the target position in the concave information track a first number of times, the first number corresponding to a first sector number which represents the number of sectors of the reproduction quality signal measured in the concave information track, and changes the target position in the convex information track a second number of times, the second number corresponding to a second sector number which represents the number of sectors of the reproduction quality signal measured in the convex information track. The first sector number and the second sector number are substantially equal to each other.
In one embodiment of the invention, when reproduction of desired information results in failure, the reproduction quality signal measuring section changes the target position in the vicinity of the information track on which the desired information which was not reproduced is recorded.
In one embodiment of the invention, the information carrier includes a first division section and a second division section obtained by dividing one rotation of track, the reproduction quality signal measuring section changes the target position in the first division section, measures a value of a first division section reproduction quality signal corresponding to each of the target positions changed in the first division section, changes the target position in the second division section, and measure a value of a second division section reproduction quality signal corresponding to each of the target positions in the second division section. The reproduction quality signal characteristic determining section determines a characteristic of the first reproduction quality signal based on the value of the first division section reproduction quality signal, and determines a characteristic of the second reproduction quality signal based on the value of the second division section reproduction quality signal. The target position searching section searches for a first optimum target position at which the first reproduction quality signal has an optimum value based on a determination result of the characteristic of the first reproduction quality signal obtained by the reproduction quality signal characteristic determining section, and searches for a second optimum target position at which the second reproduction quality signal has an optimum value based on a determination result of the characteristic of the second reproduction quality signal obtained by the reproduction quality signal characteristic determining section.
In one embodiment of the invention, the target position searching section determines the optimum target position based on an average value of the first optimum target position and the second optimum target position.
In one embodiment of the invention, the reproduction quality signal measuring section smoothes the first optimum target position and the second optimum target position with a prescribed time constant and outputs the smoothing result to the focus controller.
Thus, the invention described herein makes possible the advantages of providing (1) an optical disk apparatus for guaranteeing stable focus control and reproduction signal performance by executing an optimum method of target position search based on the characteristic of the reproduction quality signal and thus finding the optimum target position quickly with high precision; and (2) an optical disk apparatus for setting an optimum target position for a medium, such as a DVD-RAM disk, having a convex land track and a concave groove track even when the jitter or reproduction signal amplitude characteristic is significantly different between the land track and the groove track due to factors such as, for example, optical aberration and bean profile.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.